Access SQL Query to Count Unique Occurrences of One Field Matching Multiple Parameters/Rows, Some Identical - sql

Question

Struggling with ms-access's flavor of SQL queries still, though I've made some progress (thanks to y'all). I have an event log table like this:
Logs Table
logID (auto#)
modID (str)
relID (str)
DateTime (date)
TxType (short)
1
1234
22.3
10/1/22 0800
6
2
1234
22.3
10/1/22 0900
7
3
1234
22.3
10/1/22 1000
13
4
1234
22.3
10/1/22 1100
15
5
4321
22.3
10/1/22 0830
1
6
4321
22.3
10/1/22 0930
13
7
4321
22.3
10/1/22 1030
15
8
4321
22.3
10/1/22 1130
13
9
1234
23.1
11/1/22 0800
1
10
1234
23.1
11/1/22 0900
15
11
1234
23.1
11/1/22 1000
13
12
1234
23.1
11/1/22 1100
15
13
4321
23.1
11/1/22 0830
13
14
4321
23.1
11/1/22 0930
7
15
4321
23.1
11/1/22 1030
13
16
4321
23.1
11/1/22 1130
15
What I need to do is:
filter the table by relID, then
count the number of modID's that have a 15 txType as the last/most recent chronological event in their rows.
So ideally I'd filter e.g. by relID=23.1 and get these results (but not logID # 10 for example) and then count them:
logID (auto#)
modID (str)
relID (str)
DateTime (date)
TxType (short)
12
1234
23.1
11/1/22 1100
15
16
4321
23.1
11/1/22 1130
15
As part of another function I have been able to count any modID's having a single txType successfully using
SELECT COUNT(*)
FROM (
SELECT DISTINCT Logs.modID, Logs.relID
FROM Logs
WHERE ((Logs.relID='23.1') AND ((Logs.TxType=13)))
);
Another stackoverflow user (exception - thanks!) showed me how to get the last event type for a given modID, relID combination using
SELECT TOP 1 TxType
FROM Logs
WHERE (((Logs.modID=[EnterModID])) AND ((Logs.relID=[EnterRelID])))
ORDER BY DateTime DESC;
But I'm having trouble combining these two. I know I can combine COUNT and GROUP BY but Access treats GROUP BY very particularly, and I'm not sure how to use SELECT TOP to get the latest events for each modID rather than just the latest events in the table, period.

Answer 1

This should give you the logID from the row with the latest DateTime for each combination of modIDand your target relID:
PARAMETERS which_relID Text(255);
SELECT DISTINCT
(
SELECT TOP 1 logID
FROM Logs
WHERE modID=l.modID AND relID=l.relID
ORDER BY [DateTime] DESC
) AS latest_modID
FROM Logs AS l
WHERE l.relID=[which_relID]
Use it as a subquery which you INNER JOIN to your Logs table. Note the subquery evaluates rows regardless of TxType. So have the parent query select only rows whose TxType = 15
PARAMETERS which_relID Text(255);
SELECT l2.*
FROM
Logs AS l2
INNER JOIN
(
SELECT DISTINCT
(
SELECT TOP 1 logID
FROM Logs
WHERE modID=l.modID AND relID=l.relID
ORDER BY [DateTime] DESC
) AS latest_modID
FROM Logs AS l
WHERE l.relID=[which_relID]
) AS sub
ON l2.logID=sub.latest_modID
WHERE l2.TxType=15;
Note I moved the PARAMETERS clause into the parent query. But you can eliminate it altogether if you believe it's causing trouble.
DateTime is a reserved word. I enclosed it in square brackets to ensure Access understands we mean the name of an object.
Using your sample data, I get these 2 rows when I supply 23.1 for the query parameter:
logID
modID
relID
DateTime
TxType
12
1234
23.1
11/1/2022 11:00:00 AM
15
16
4321
23.1
11/1/2022 11:30:00 AM
15
I get a single row with 22.3 for the parameter:
logID
modID
relID
DateTime
TxType
4
1234
22.3
10/1/2022 11:00:00 AM
15